This invention relates to a method of manufacturing a magnetic recording medium used as a recording medium for an information processing apparatus and the like, and a method of manufacturing a substrate thereof.
Recently, a magnetic disk has been used as an information recording medium. The magnetic disk is structured by forming a thin-film, such as, a magnetic layer, on a substrate. In this event, an aluminum substrate or a glass substrate has been generally used as the substrate.
However, the glass substrate, which can further narrow a space (namely, a flying height with respect to a magnetic head) between a magnetic head and a magnetic recording medium in comparison with the aluminum substrate, has been gradually replaced by the aluminum substrate in accordance with high recording density in the recent years.
Such a glass substrate is generally manufactured by chemically strengthening to enhance strength and endure for impact when the glass substrate is mounted for a magnetic disk drive. Further, a surface of the glass substrate is polished with high accuracy so as to lower the flying height of the magnetic head to the utmost. Thereby, high recording density has been realized.
In the meantime, a thin-film head has been recently replaced by a magneto-resistive head (namely, MR head) in the magnetic head to realize the high recording density other than the glass substrate.
High surface flatness of the magnetic disk is required to realize a low flying height necessary for the above-mentioned high recording density. In addition, when the MR head is used, the surface of the magnetic recording medium must have high flatness from the viewpoint of thermal asperity.
When the magnetic disk has projections on the surface of the magnetic disk, the MR head is affected by the projections to generate heat for the MR head, and resistance value of the head is fluctuated to cause to occur an error operation for electro-magnetic conversion by the heat. This phenomenon is defined as the above-mentioned thermal asperity.
Further, even when the surface of the magnetic disk has the high flatness, if the surface of the magnetic disk has the projections which cause the thermal asperity, head crush brings about by the projections, and a magnetic film constituting the magnetic disk is peeled in the cause of the head crush. Thus, the projections give an adverse affect for the magnetic disk.
Thus, demand has been gradually enhanced about the high surface flatness of the magnetic disk to realize the low flying height and prevent the head crush and the thermal asperity. The substrate surface having the high flatness is finally required to obtain the high surface flatness of the magnetic disk. However, the high recording density can be no longer realized only by polishing the substrate surface with the high accuracy.
More specifically, even when the substrate surface is polished with the high accuracy, the high flatness can not be realized in case that contaminants are attached on the substrate. Although the contaminants have been naturally and conventionally removed, the contaminants, which have been placed on the substrate and conventionally have been permitted, cause a problem in a recent level with respect to the high recording density.
In this case, excessively small iron powder and stainless steel piece, which can not remove by the use of a normal washing process, are exemplified as this kind of contaminant. For example, it has been confirmed that when a chemical strengthening process is performed on the condition that particles, such as, the iron powders are attached on the glass substrate or that the particles are attached on the glass substrate in the chemical strengthening processing liquid, irons are strongly attached on the glass substrate to form island portions (namely, the projections) through oxidation reaction occurred in the chemical strengthening process and heat applied in the process.
It has been found out that when the thin-film, such as, the magnetic film is laminated on the glass substrate, the island portions (projections) are formed on the surface of the magnetic disk to prevent the low flying height and to occur the head crush and the thermal asperity.
Therefore, investigation has been fully made about a cause in which such fine iron powders are attached to the glass substrate. As a result, it has been confirmed that the iron powders are contained in a chemical strengthening chamber for performing the chemical strengthening process, and in particular, a large number of iron powders are contained in a chemical strengthening salt itself.
More specifically, when the number of the iron powders has been investigated for each generation factor, the number of the iron powders contained in the chemical strengthening salt itself before the chemical strengthening salt (sodium nitrate or potassium nitrate) is prepared to make the chemical strengthening processing liquid is excessively high.
Further, it has been found out that the chemical strengthening salt itself contains the other particles which give an adverse affect for the information recording medium by attaching to the glass substrate for the information recording medium.
Meanwhile, disclosure has been made about a technique for removing the iron powders contained in atmosphere of the chemical strengthening chamber for performing the chemical strengthening process and preventing the iron powders from contaminating the chemical strengthening processing liquid in Japanese Unexamined Patent Publication No. H10-194785.
Another disclosure has been made about a technique for removing the iron powders contaminated from the atmosphere in the chemical strengthening chamber into the chemical strengthening processing liquid by filtering the chemical strengthening processing liquid by the use of a filter having superior corrosion resistance to high temperature, such as, a microsieve (namely, wire cloth in which holes are opened by etching) in Japanese Unexamined Patent Publication No. H10-194786.
In this event, the former method is effective for removing the iron powders contained in the atmosphere in the chemical strengthening chamber for performing the chemical strengthening process.
Although the latter method has a constant effect, the number of the iron powders contained the chemical strengthening salt itself before making the chemical strengthening processing liquid is excessively high as mentioned above, and as a result, the latter method is not sufficiently effective for removing the iron powders.
Further, the latter method is not enough to remove the other particles which attach to the glass substrate for the information recording medium in the chemical strengthening process and give the adverse affect for the information recording medium.
Moreover, the chemical strengthening process is carried out by replacing ions contained in the glass by ions contained in original liquid for ion exchange, or distribution with respect to index of refraction is adjusted in a glass substrate for an electron device (including a glass substrate for a photomask, a glass substrate for a phase shift mask, or a glass substrate for an information recording medium, and hereinafter, will be used as the same meaning) or a glass substrate for an optical device in addition to above-mentioned glass substrate for the information recording medium.
In such glass substrates, the original liquid for ion exchange contains Fe and Cr, and thereby, the efficiency of ion exchange is lowered or the island portions are formed. For example, the island portions shield a light beam, and as a result, a desired characteristic may not obtained.
It is therefore an object of this invention to provide a method of manufacturing a glass substrate for a magnetic recording medium which is capable of effectively suppressing attachment of particles which attach to a glass substrate for an information recording medium in a chemical strengthening process and which give an adverse affect for an information recording medium.
In particular, it is another object of this invention to provide a method of manufacturing a glass substrate for a magnetic recording medium which is capable of effectively suppressing formation of projections formed by attachment of fine iron powders to a glass substrate in a chemical strengthening process.
It is still another object of this invention to provide a method of manufacturing a magnetic recording medium which is capable of effectively suppressing attachment of particles which attach to a glass substrate for an information recording medium in a chemical strengthening process and which give an adverse affect for an information recording medium, and therefore, of obtaining an information recording medium having high quality and a slight of defects.
It is further another object of this invention to provide a method of manufacturing a magnetic disk which is capable of realizing a low flying height and preventing head crush and thermal asperity.
It is still other object of this invention to provide a method of manufacturing an electron device or an optical device which is capable of effectively suppressing attachment of particles, which give an adverse affect by attaching to a glass substrate for an electron device or a glass substrate for an optical device in an ion exchange step, and therefore, of having a slight of defects.
Inventors have proceeded research and development to achieve the above-mentioned objects. As a result, it has been found out that island portions (projections) are formed even when a size of an iron powder (including iron oxide or stainless steel) is 1 xcexcm or less (for example, 0.2 xcexcm). Further, it is excessively effective to previously remove particles, such as, the iron powders contained in chemical strengthening salt itself.
To this end, it has been found out that it is extremely effective to perform quantitative analysis of iron or chromium contained in the chemical strengthening salt, and thereby, this invention has been completed.
Namely, this invention has the following structures.
(Structure 1)
In a method of manufacturing a glass substrate for an information recording medium including a step for chemically strengthening the glass substrate by contacting the glass substrate with chemical strengthening processing liquid containing a chemical strengthening salt, concentration of Fe and Cr is 500 ppb or less in said chemical strengthening salt, respectively. The concentration is detected by the use of an ICP (Inductively Coupled Plasma) emission spectrometry analyzing method or a fluorescent X-ray spectroscopy analyzing method.
(Structure 2)
In the method of the structure 1, the concentration of Fe and Cr is 100 ppb or less in said chemical strengthening salt, respectively. The concentration is detected by the use of the ICP (Inductively Coupled Plasma) emission spectrometry analyzing method or the fluorescent X-ray spectroscopy analyzing method.
(Structure 3)
In the method of the structure 1, the concentration of Fe and Cr are 20 ppb or less in said chemical strengthening salt, respectively. The concentration is detected by the use of the ICP (Inductively Coupled Plasma) emission spectrometry analyzing method or the fluorescent X-ray spectroscopy analyzing method.
(Structure 4)
In the method of either one of structures 1 through 3, quantitative analysis of element and concentration of impurity such as particles of chemical strengthening of the chemical strengthening salt is carried out by the use of the an ICP (Inductively Coupled Plasma) emission spectrometry analyzing method or the fluorescent X ray spectroscopy analyzing method on the basis of a calibration curve. The calibration curve is determined by standard solutions each having different concentrations of Fe, Cr. The concentrations of Fe, Cr of chemical strengthening salt are determined by the calibration curve, after analyzing intensity of the atomic emissions of filtering solution dissolved with the chemical strengthening salt in solvent by a filter, dissolving particles captured by the filter in acid, and measuring a known concentration sample in advance.
(Structure 5)
In a method of manufacturing a glass substrate for an information recording medium including a step for chemically strengthening the glass substrate by contacting the glass substrate with chemical strengthening processing liquid containing chemical strengthening salt, the number of particles having a particle diameter of 0.2 xcexcm or more is 120000/g or less in the chemical strengthening salt. The number is determined from a difference between the particle number in a sample dissolved with the chemical strengthening salt in a reference liquid measured by the use of a liquid particle counter and the particle number in the reference liquid.
(Structure 6)
In a method of manufacturing a glass substrate for an information recording medium including a step for chemically strengthening the glass substrate by contacting the glass substrate with chemical strengthening processing liquid containing chemical strengthening salt, the number of particles having a particle diameter of 0.2 xcexcm or more is 900/mm2 or less in the chemical strengthening salt when the particles contained in the chemical strengthening salt of 1 g are captured by a filter having a minimum capturing particle diameter of 0.2 xcexcm and a diameter of 13 mm in case that secondary electron image or back-scattered electron image is observed by a scanning electron microscope (SEM) by the use of a secondary electron detector or a back-scattered electron image detector.
(Structure 7)
In a method of the structure 6, the number of the particles is 500/mm2 or less in the chemical strengthening salt.
(Structure 8)
In a method of the structure 6, the number of the particles is 30/mm2 or less in the chemical strengthening salt.
(Structure 9)
In a method of manufacturing a glass substrate for an information recording medium including a step for chemically strengthening the glass substrate by contacting the glass substrate with chemical strengthening processing liquid containing chemical strengthening salt, the chemical strengthening salt does not become a black color or a gray color or a red brown color when the chemical strengthening salt is analyzed by the use of calorimetric analysis.
(Structure 10)
In a method of manufacturing a glass substrate for an information recording medium including a step for chemically strengthening the glass substrate by contacting the glass substrate with chemical strengthening processing liquid containing chemical strengthening salt, when solution dissolved with said chemical strengthening salt in solvent is filtered by a filter, and particles are captured by the filter, a color concentration of the filter becomes a constant reference value or less in the chemical strengthening salt.
(Structure 11)
In a method of inspecting chemical strengthening salt, the analyzing method of the structures 1 through 10 is used.
(Structure 12)
In a method of the structures 1 through 10, the glass substrate for the information recording medium comprises a glass substrate for a magnetic disk.
(Structure 13)
In a method of the structure 12, the glass substrate for the magnetic disk comprises a glass substrate for a magnetic disk which is used by combining with a magneto-resistive head (MR head) or a giant magneto-resistive head (GMR head).
(Structure 14)
In a method of manufacturing an information recording medium, at least a recording layer is formed on the glass substrate obtained by the manufacturing method of the glass substrate for the information recording medium of the structures 1 through 10.
(Structure 15)
In a method of manufacturing a magnetic disk, at least a magnetic layer is formed on the glass substrate obtained by the manufacturing method of the glass substrate for the information recording medium of the structures 1 through 10.
(Structure 16)
In a method of manufacturing an optical glass substrate, including the step of exchanging ions in a glass component with ions in an ion exchange processing liquid by dipping the glass component in the ion exchange processing liquid, a salt satisfying the conditions described in any one of the structures 1 through 3 and 5 through 10 is used for the ion exchange processing liquid.
(Structure 17)
In a method of the structure 16, the optical glass substrate is a glass substrate for an electronic device or a glass substrate for an optical device and the ion exchange processing liquid is a chemical strengthening processing liquid containing a chemical strengthening salt.
(Structure 18)
In a method of manufacturing a glass substrate for an information recording medium including a chemical strengthening step for strengthening the glass substrate by replacing a part of first ions contained in the glass substrate by second ions in processing liquid having an ion diameter larger than the first ion by contacting the glass substrate with chemical strengthening processing liquid containing a chemical strengthening salt, content of particles is suppressed in order to prevent generation of thermal asperity in the chemical strengthening salt. The particles cause the thermal asperity.
(Structure 19)
In a method of manufacturing a glass substrate for an information recording medium including a chemical strengthening step for strengthening the glass substrate by replacing a part of first ions contained in the glass substrate by second ions in a processing liquid having an ion diameter larger than the first ion by contacting the glass substrate with chemical strengthening processing liquid containing chemical strengthening salt, the number of particles having a particle diameter of 0.2 xcexcm or more contained in the chemical strengthening salt is 12000/ml or less.
(Structure 20)
In a method of the structure 19, a ratio of the particles having the particle diameter of 0.2 xcexcm or more is 25% or less in the chemical strengthening salt.
(Structure 21)
In a method of the structure 19 or 20, the number of particles having a particle diameter of 0.2 xcexcm or more contained the chemical strengthening salt is 4000/ml or less.
(Structure 22)
In a method of the structures 18 through 21, the particle contains iron.
(Structure 23)
In a method of the structures 18 through 22, the glass substrate for the information recording medium comprises a glass substrate for a magnetic disk.
(Structure 24)
In a method of the structure 23, the glass substrate for the magnetic disk comprises a glass substrate for a magnetic disk which is used by combining with a magneto-resistive head (MR head) or a giant magneto-resistive head (GMR head).
(Structure 25)
In a method of manufacturing an information recording medium, at least a recording layer is formed on the glass substrate obtained by the manufacturing method of the glass substrate for the information recording medium of the structures 18 through 24.
(Structure 26)
In a method of manufacturing an magnetic disk, at least a magnetic layer is formed on the glass substrate obtained by the manufacturing method of the glass substrate for the information recording medium of the structures 18 through 24.
(Structure 27)
A method of manufacturing a glass substrate for a magnetic disk, comprising the steps of:
preparing a glass substrate;
judging whether or not the amount of particles contained in a chemical strengthening salt itself is not greater than a predetermined reference value;
reducing, if the predetermined reference value is exceeded, the amount of particles contained in the chemical strengthening salt itself to a level not greater than the predetermined reference value;
preparing a chemical strengthening processing liquid by mixing the chemical strengthening salt containing the particles in an amount not greater than the predetermined reference value; and
chemically strengthening the glass substrate by replacing a part of first ions contained in the glass substrate by second ions contained in the processing liquid and having an ion diameter larger than that of the first ions by contacting the glass substrate with the chemical strengthening processing liquid.
(Structure 28)
In the method of the structure 27, the predetermined reference value is determined by preliminarily obtaining correlation between the amount of particles contained in the chemical strengthening salt itself and a glide height, selecting, with reference to the correlation, a particular amount of particles corresponding to a desired glide height, and setting the particular amount as the predetermined reference value.
(Structure 29)
In a method of manufacturing a magnetic disk, at least a magnetic layer is formed on a principal surface of the glass substrate for the magnetic disk of the structure 27 or 28.
According to the structures 1-3, the concentration of Fe and Cr is 500 ppb or less in the chemical strengthening salt, respectively. The concentration is detected by the use of an ICP (Inductively coupled Plasma) emission spectrometry analyzing method or a fluorescent X-ray spectroscopy analyzing method.
Consequently, formation of an island portion can be effectively suppressed. In this case, fine iron powder in chemical strengthening processing liquid is attached to the glass substrate, and thereby, the island portion is formed. Therefore, a low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
When the concentration of Fe and Cr exceeds 500 ppb, a ratio, in which the island portion is formed, becomes excessively high, and the height of the island portion and the density of the island portions become high during the chemical strengthening step. Further, the faulty rate becomes high in the glide test of the 1.2 xcexcm inch height, and the probability of reproduction error due to the thermal asperity also becomes high.
From the same view, the concentration of Fe and Cr is preferably 250 ppb or less, and more preferably, 100 ppb or less, 20 ppb or less, 10 ppb or less, 5 ppb or less, and 1 ppb or less.
In the ICP (Inductively Coupled Plasma) emission spectrometry analyzing method, elements to be analyzed and contained in the sample are vaporized and excited by inductively coupled plasma generated by inductively coupling high frequency power, and the quantitative analysis is carried out by measuring the obtained emission intensity in an atom spectrum line (JIS K 0116).
According to the structure 4, quantitative analysis of element and concentration of the chemical strengthening salt is carried out by the use of the an ICP (Inductively Coupled Plasma) emission spectrometry analyzing method or the fluorescent X-ray spectroscopy analyzing method on the basis of a calibration curve. The calibration curve is determined by filtering solution dissolved with the chemical strengthening salt in solvent by a filter, dissolving particles captured by the filter in acid, and measuring a known concentration sample in advance.
Consequently, the metal based particles, such as, iron or chromium, are dissolved in acid, and the quantitative analysis can be performed by the ICP (Inductively Coupled Plasma) emission spectrometry analyzing method having high sensitivity.
According to the structure 5, the particle number is determined from the difference between the particle number in the sample dissolved with the chemical strengthening salt in the reference liquid and the particle number in the reference liquid (namely, blank).
Thereby, an accurate measuring value of the particle number having a slight of variation can be obtained, and an accurate judgement is possible on the basis of the measuring value.
Further, the number of particles having a particle diameter of 0.2 xcexcm or more is 120000/g or less in the chemical strengthening salt. In consequence, the attachment of the particles, which give an adverse affect for the information recording medium by attaching to the glass substrate for the information recording medium in the chemical strengthening processing liquid, can be effectively suppressed.
In particular, fine iron powder in the chemical strengthening processing liquid attach to the glass substrate. In this case, the formation of the island portions can be effectively suppressed.
In this event, the particle has a particle diameter of 0.2 xcexcm or more. This is because the particles having the particle diameter of not exceeding 0.2 xcexcm do not give an affect for the formation of the island portion which causes the thermal asperity.
When the number of particles having a particle diameter of 0.2 xcexcm or more exceeds 120000/g, the fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate, and a ratio, in which the island portion is formed, becomes high. Consequently, the number of the island portions becomes high, and the height and density of the island portion also becomes high. Further, this is not preferable because a ratio, which the thermal asperity and the head crush occur, becomes high.
Similarly, when the number of particles having a particle diameter of 0.2 xcexcm or more exceeds 120000/g, the attachment number of the particles, which give an adverse affect for the information recording medium by attaching to the glass substrate for the information recording medium in the chemical strengthening processing liquid, becomes high. This is not preferable.
From the same viewpoint, the number of particles having a particle diameter of 0.2 xcexcm or more contained in the chemical strengthening salt is preferably 8000/g or less, and more preferably, 4000/g or less. This reason is explained as follows. Namely, the number of the particles contained in the chemical strengthening salt is directly reflected for the generation of the island portion in the chemical strengthening processing liquid and the attachment of the particles. Therefore, the probability for generating the island portions or the attachment number of the particles can be reduced by reducing the number of the particles contained in the chemical strengthening salt.
Further, the density of the island portions is desirably 0.0021mm2 or less, and more desirably, 0.0003/mm2 or less.
According to the structures 6xcx9c8, when secondary electron image or back-scattered electron image is observed by a scanning electron microscope (SEM) by the use of a secondary electron detector or a back-scattered electron detector, the number of particles (such as iron powder, stainless steel piece) having a particle diameter of 0.2 xcexcm or more is 900/mm2 or less in the chemical strengthening salt when the particles contained in the chemical strengthening salt of 1 g are captured by a filter having a minimum capturing particle diameter of 0.2 xcexcm and a diameter of 13 mm.
Thereby, the fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate and the formation of the island portion can be effectively suppressed. Consequently, the low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
When the number of the particles (such as iron powder and stainless steel piece) exceeds 500/mm2, a ratio, in which the island portion is formed, becomes excessively high, and the height and density of the island portion also become high. Further, the faulty rate becomes high in the glide test of the 1.2 xcexcinch height, and the probability of the reproduction error due to the thermal asperity also becomes high. The number of the particles (such as the iron powder and stainless steel piece) is preferably 500/mm2 or less, 300/mm2 or less, 100/mm2 or less, 30/mm2 or less, and more preferably, 10/mm2 or less.
According to the structure 9, the chemical strengthening salt does not become a black color or a gray color or a red brown color when the chemical strengthening salt is analyzed by the use of colorimetric analysis.
Thereby, the fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate and the formation of the island portion can be effectively suppressed. Consequently, the low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
When the chemical strengthening salt becomes the black color or the gray color or the red brown color in case that the chemical strengthening salt is analyzed by the use of the calorimetric analysis, a ratio, in which the island portion is formed during the chemical strengthening step, becomes excessively high, and the height and density of the island portion also become high. Further, the faulty rate becomes high in the glide test of the 1.2 xcexcinch height, and the probability of the reproduction error due to the thermal asperity also becomes high.
According to the structure 10, the solution of the chemical strengthening salt is filtered by the filter, particles are captured by the filter, and the color concentration of the filter becomes a constant reference value or less in the chemical strengthening salt.
Thereby, the fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate and the formation of the island portion can be effectively suppressed. Consequently, the low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
When the color concentration of the filter is denser than the constant reference value, a ratio, in which the island portion is formed during the chemical strengthening step, becomes excessively high, and the height and density of the island portion also become high. Further, the faulty rate becomes high in the glide test of the 1.2 xcexcinch height, and the probability of the reproduction error due to the thermal asperity also becomes high.
According to the structure 11, the analyzing method of the structures 1 through 10 is used as the inspecting method of the chemical strengthening salt.
According to the structure 12, the glass substrate for the information recording medium is a glass substrate for a magnetic disk. Thereby, the formation of the island portion, which causes the head crush, can be effectively suppressed. Therefore, the low flying height can be realized, and the head crush and the thermal asperity can be prevented in the magnetic disk.
According to the structure 13, the glass substrate for the magnetic disk may be a glass substrate for a magnetic disk which is used by combining with a magneto-resistive head. Thereby, the formation of the island portion, which causes the thermal asperity and the head crush, can be effectively suppressed. As a result, the low flying height can be realized. When the magneto-resistive head is used, this is particularly effective because the low flying height is required.
According to the structure 14, the glass substrate obtained by the manufacturing method of the glass substrate for the information recording medium of the structures 1 through 10 is used. Thereby, the attachment of the particles, which give an adverse affect for the information recording medium by attaching to the glass substrate for the information recording medium in the chemical strengthening processing liquid, can be effectively suppressed. Further, the information recording medium having high quality and a slight of defects can be obtained.
According to the structure 15, the glass substrate obtained by the manufacturing method of the glass substrate for the information recording medium of the structures 1 through 10 is used.
Thereby, the fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate and the formation of the island portion can be effectively suppressed. Consequently, the low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
According to the structure 16-17, in a method of manufacturing an optical glass substrate, including the step of exchanging ions in a glass component with ions in an ion exchange processing liquid by dipping the glass component in the ion exchange processing liquid, a salt satisfying the conditions described in any one of the structures 1 through 3 and 5 through 10 is used for the ion exchange processing liquid. The optical glass substrate is a glass substrate for an electronic device or a glass substrate for an optical device and the ion exchange processing liquid is a chemical strengthening processing liquid containing a chemical strengthening salt.
Consequently, the island portion is not formed on the chemically strengthened glass substrate or the glass substrate in which distribution with respect to index of refraction is adjusted, and the electron device or the optical device having high quality can be obtained.
According to the structure 16, the original liquid for the ion exchange may be a chemical strengthening processing liquid containing chemical strengthening salt. This is effective to fabricate the chemically strengthened glass (used in the electron device or the optical device). Furthermore, the reduction of the efficiency of the ion leakage can be suppressed/
According to the structure 18, content of particles, which are contained in the chemical strengthening salt itself and cause the thermal asperity, is suppressed.
Thereby, the fine iron powder in the chemical strengthening processing liquid attached to the glass substrate and the formation of the island portion can be effectively suppressed. Consequently, the low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
According to the structure 19, the number of particles having a particle diameter of 0.2 xcexcm or more is 12000/ml or less in the chemical strengthening salt. In consequence, the attachment of the particles, which give an adverse affect for the information recording medium by attaching to the glass substrate for the information recording medium in the chemical strengthening processing liquid, can be effectively suppressed.
In particular, fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate. The formation of the island portions can be effectively suppressed.
In this case, the particle has a particle diameter of 0.2 xcexcm or more. This is because the particles having the particle diameter of not exceeding 0.2 xcexcm do not give an affect for the formation of the island portion which causes the thermal asperity.
When the number of particles having a particle diameter of 0.2 xcexcm or more exceeds 12000/ml, the fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate, and a ratio, in which the island portion is formed, becomes high. Consequently, the number of the island portions also becomes high, and the height and density of the island portion also becomes high. Further, this is not preferable because a ratio, which the thermal asperity and the head crush occur, becomes high.
Similarly, when the number of particles having a particle diameter of 0.2 xcexcm or more exceeds 12000/ml, the attachment number of the particles, which give an adverse affect for the information recording medium by attaching to the glass substrate for the information recording medium in the chemical strengthening processing liquid, becomes high. This is not desirable.
From the same viewpoint, the number of particles having a particle diameter of 0.2 xcexcm or more contained in the chemical strengthening salt is preferably 8000/ml or less, and more preferably, 4000/ml or less. This reason is explained as follows. Namely, the number of the particles contained in the chemical strengthening salt is directly reflected for the generation of the island portion in the chemical strengthening processing liquid and the attachment of the particles. Therefore, the probability for generating the island portions or the attachment number of the particles can be reduced by reducing the number of the particles contained in the chemical strengthening salt.
Further, the density of the island portions is desirably 0.002/mm2 or less, and more desirably, 0.0003/mm2 or less.
In this case, the number of the particles contained in the chemical strengthening salt was measured by the following predetermined method.
Namely, the chemical strengthening salt (the potassium nitrate and the sodium nitrate) was dissolved in the super pure water of 90 ml with 10 g respectively. Herein, it is to be noted that the super pure water means water which is sufficiently cleaned and does not contain the particles that give an affect for the measurement.
The solution was successively measured three times by the particle counter (made by Lion Ltd. or PMS Ltd.) for the liquid with 5 ml.
Further, the number of the particles (the total of the particle number in each particle size) contained per 1 ml was determined and converted, and these average values were decided as the particle number. In this case, the total of the particle number corresponds to the total of the number of the particles which exist in a range of each particle size which is arbitrarily determined.
According to the structure 20, a ratio of the particles, which give a large affect for the formation the island portion (projection) and have a large particle diameter (specifically, the particle diameter of 0.2 xcexcm or more) is 25% or less in the chemical strengthening salt. Thereby, the formation of the island portion (projection) can be effectively prevented. From the same viewpoint, the ratio is preferably 20% or less, and more preferably, 15% or less.
According to the structure 21, the number of particles having a particle diameter of 2 xcexcm or more contained said chemical strengthening salt is 4000/ml or less. Thereby, the formation of the island portion (projection) can be further effectively prevented.
This reason is explained as follows. Namely, the particle having the particle diameter of 2 xcexcm or more gives a strong affect in comparison with the particle having not exceeding 2 xcexcm. Further, the particle diameter of the particle of iron, which causes the thermal asperity, is about 2 xcexcm or more.
According to the structure 22, the particle contains a particle of iron. When the particle contained in the chemical strengthening salt was analyzed, O, Na, Mg, Al, Si, Cl, Fe, Cr and the like were detected. In particular, when the particle is Fe (iron), and the particle (iron) is attached to the glass substrate in the chemical strengthening processing liquid, the island portion (projection) dissolved with iron is formed on the glass substrate by the oxidation reaction occurred in the chemical strengthening process and the heat applied in this process. These island portions cause the thermal asperity and the head crush with high probability.
Meanwhile, when the particle has a relatively large size, the particles are dissolved to form the island portions (projections). In the meantime, the particle has a relatively small size, the particles aggregate and dissolve to form the island portions (projections). Such phenomenon has been confirmed by a microscope.
Therefore, a remarkable effect particularly appears by controlling quantity (the number) of the particles, such as, the iron contained in the chemical strengthening salt in the magnetic disk.
Further, the particle of the iron contains the iron oxide and SUS in addition to the iron. Moreover, metal, such as, Cr and Al is exemplified as material of the particle for forming the island portion (projection) by the above-mentioned oxidation reaction and the heat.
According to the structure 23, when the glass substrate for the information recording medium is a glass substrate for a magnetic disk, the formation of the island portion, which causes the head crush, can be effectively suppressed. In consequence, the low flying height can be achieved and the head crush can be prevented.
According to the structure 24, when the glass substrate for the magnetic disk is a glass substrate for a magnetic disk which is used by combining with a magneto-resistive head, the formation of the island portion, which causes the thermal asperity, can be effectively suppressed. As a result, the low flying height can be realized. When the magneto-resistive head is used, this is particularly effective because the low flying height is required.
According to the structure 26, the glass substrate obtained by the manufacturing method of the glass substrate for the information recording medium of the structures 18 through 24 is used.
Thereby, the fine iron powder in the chemical strengthening processing liquid attaches to the glass substrate and the formation of the island portion can be effectively suppressed. Consequently, the low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
According to the structure 27 and 28, a correlation between a content of particles contained in chemical strengthening salt itself and a glide height is determined in advance. The content of the particles, which becomes a desired glide characteristic, is determined as a reference setting value from the correlation. It is judged that the content of the particles contained in the chemical strengthening salt itself is the predetermined reference setting value or less. The content of the particles contained in the chemical strengthening salt itself is set to the predetermined setting value or less when the content exceeds the reference setting value.
Thereby, chemical strengthening processing liquid can be made by preparing the chemical strengthening salt. Therefore, the generation of the island portion or the attachment of the particles can be reduced in the chemical strengthening process.
In this case, the reference setting value can be selected in accordance with a permitted level of defect required for the information recording medium. Further, the reference setting value is determined such that a magnetic head is arranged in opposition to a principal surface of a magnetic disk (or a glass susbstrate), the magnetic disk is relatively moved for the magnetic disk (or the glass substrate) with a predetermined height, and a desired glide height characteristic is obtained.
In other words, the reference setting value is determined on the basis of the result of the glide test, and thereby, the head crush or the thermal asperity can be effectively prevented. Herein, it is to be noted that the desired glide characteristic may mean that generating rate of hit and crush becomes 0% in the glide height of 1.2 xcexcinch or less.
The reference value in the structure 27 may be determined by obtaining correlation between the amount of particles contained in the chemical strengthening salt itself and a glide height, selecting, with reference to the correlation, a particular amount of particles corresponding to a desired glide height, and setting the particular amount as the reference value, as described in the structure 28. Alternatively, the reference value may be determined by obtaining the correlation between the amount of particles and the occurrence ratio of the thermal asperity, the correlation between the amount of particles and the defect ratio in the glide test, the correlation between the amount of particles and the height and the density of the island portion, and so on, selecting a particular amount of particles contained in the chemical strengthening salt itself so that the magnetic disk has desired characteristics, and setting the particular amount as the reference value.
According to the structure 29, at least a magnetic layer is formed on a principal surface of the glass substrate for the magnetic disk of the structure 27 or 28. Thereby, the low flying height can be achieved, and the head crush and the thermal asperity can be prevented in the magnetic disk.
In this case, the particle in this invention contains a particle of iron. When the particle contained in the chemical strengthening salt was analyzed, O, Na, Mg, Al, Si, Cl, Fe, Cr and the like were detected. In particular, when the particle is Fe (iron), the particle (iron) is attached to the glass substrate in the chemical strengthening processing liquid. In this case, the particles are strongly attached onto the glass substrate by the oxidation reaction occurred in the chemical strengthening process and the heat applied in this process to form the island portions (projections). These island portions cause the thermal asperity and the head crush with high probability.
Meanwhile, when the particle has a relatively large size, the particle is strongly attached to form the island portions (projections). In the meantime, the particle has a relatively small size, the particles aggregate and are strongly attached to form the island portion (projection). Such phenomenon has been confirmed by a microscope.
Therefore, a remarkable effect particularly appears by controlling quantity of the particles, such as, the iron contained in the chemical strengthening salt in the magnetic disk.
Further, the particle of the iron contains the iron oxide and the stainless steel in addition to the iron. Moreover, Ti, Al, Cl, Ce, and a glass piece are exemplified as the other material of the particle for forming the island portion (projection) by the above-mentioned oxidation reaction and the heat.
Subsequently, description will be made about the method of manufacturing the glass substrate for the information recording medium.
In this invention, quantity (the number) and concentration of the particles, such as, the iron contained in the chemical strengthening salt itself are analyzed by the above-mentioned analyzing method, and the chemical strengthening salt satisfying a reference value or less is used. This is a feature of this invention.
Thus, it is judged by the analysis that the quantity of the particles contained in the chemical strengthening salt itself falls within the range of the predetermined reference value or less. As a result of the judgement, the chemical strengthening salt of the reference value or less is prepared, and thereby, the chemical strengthening processing liquid can be made such that the quantity of the particles falls within the range the predetermined value or less. Consequently, generation of the island portions and the attachment of the particles can be reduced in the chemical strengthening processing step. Herein, it is to be noted that the reference value can be set in accordance with a permitted level of the defects required for the information recording medium.
For example, the above-mentioned reference value is determined in the following manner. Namely, the magnetic head is arranged in opposite to a principal surface of the magnetic disk (or the glass substrate), and the magnetic head is relatively moved for the magnetic disk (or the glass substrate) with a predetermined glide height to obtain a desired glide characteristic.
In other words, the head crush and the thermal asperity can be effectively prevented by determining the reference value on the basis of the result of the glide test. For example, the desired glide characteristic means that the glide height is 1.2 xcexcinch or less, and generating rate of hit or crush becomes 0%.
For instance, the particles are removed by the use of capturing means, such as, a filter on the condition that the chemical strengthening salt is dissolved in water to remove the particles contained in the chemical strengthening salt itself on the basis of the above-mentioned analysis result.
The quantity of the particles contained in the chemical strengthening salt can be controlled to the desired quantity or concentration by selecting performance (minimum capturing particle size) or the kind of the filter.
For example, the desired quantity means that the content of the particles of the particle diameter of 0.2 xcexcm or more is 12000/ml or less, or 4000/ml or less.
Further, a plurality of filters having different minimum capturing particle sizes are used. Thereby, after the particle having a large particle size is removed by the filter having a large minimum capturing particle size, the particle having a small particle size is removed by the filter having a small minimum capturing particle size.
It is unnecessary to use reagent refined with high purity as all components except for the chemical strengthening salt in this invention. In particular, the chemical strengthening salt, which is removed and cleaned only particles that gives an adverse affect for the iron powder or the information recording medium, is used, and thereby, the cost is reduced.
Naturally, although such reagent refined with high purity can be used, the cost is inevitably increased. Further, it is preferable that the chemical strengthening salt used in this invention contains no addition agent for preventing consolidation. This is because the addition agent for preventing the consolidation may contain a large number of particles.
Low temperature type chemical strengthening is preferable as the chemical strengthening method. In such low temperature type chemical strengthening, ion exchange is carried out within a region not exceeding a glass transition temperature. Potassium nitrate, sodium nitrate, or nitrate salt mixed them, potassium sulfate, sodium sulfate, or sulfate salt mixed them, or NaBr, KBr and salt mixed them can be used as alkali solvent salt used in the chemical strengthening processing liquid.
In this case, aluminosilicate glass, soda-lime glass, and borosilicate glass are exemplified as the glass substrate. A glass substrate for a magnetic recording medium, a glass substrate for an optical recording medium, and a glass substrate for an electro-optical recording medium are exemplified as the glass substrate for the information recording medium.
In particular, this invention achieves a remarkable effect with respect to the magnetic disk for the magneto-resistive head and the substrate thereof.
Subsequently, description will be made about a method of manufacturing the magnetic recording medium (the magnetic disk) according to this invention.
In this invention, the magnetic recording medium is manufactured by forming at least a magnetic layer on the above glass substrate for the magnetic recording medium according to this invention.
According to this invention, the attachment of the particles, which cause the thermal asperity or the head crush, can be effectively suppressed. In consequence, when the magnetic recording medium having the magnetic layer on the glass substrate is fabricated, it is difficult to form the island portions formed by the particles, which cause the thermal asperity, on the principal surface of the glass substrate. Thereby, the thermal asperity or the head crush can be prevented with higher level.
For example, the low glide height of the 1.2 xcexcinch or less can be also realized because the island portions are not formed. In particular, the magnetic recording medium, which reproduces by the magneto-resistive head, can sufficiently achieve function as the magneto-resistive head. Further, the magnetic recording medium can sufficiently achieve performance thereof as the magnetic recording medium of CoPt base and the like because it can be suitably used for the magneto-resistive head.
Moreover, no defect occurs for a film, such as, the magnetic layer by the particles which cause the thermal asperity. As a result, no error due to the defect takes place.
The magnetic recording medium generally has the predetermined flatness and surface roughness, and is manufactured by successively laminating an underlying layer, an magnetic layer, a protection layer, and a lubricant layer on the glass substrate for the magnetic disk in which the chemical strengthening process is performed for the surface as needed.
The underlying layer is selected in relation to the magnetic layer. At least one metal selected from a group consisting of nonmagnetic metals, Cr, Mo, Ta, Ti, W, V, B, Al, Ni may be used as a material of the underlying layer (including a seed layer). The metal Cr or the Cr alloy is preferably used as the material of the underlying layer to enhance a magnetic characteristic where the magnetic layer includes Co as a main component. In addition, the underlying layer may not always be formed by a single layer but may be formed by a multi-layer composed of a plurality of identical or different layers. For example, deposition may be made as the underlying layer formed by the multi-layer ,such as, Cr/Cr, Cr/CrMo, Cr/CrV, NiAl/Cr, NiAl/CrMo, and NiAl/CrV.
In this invention, no limitations are imposed as to the magnetic layer also.
The magnetic layer may be, for example, a layer which contains Co as a main component and which has a composition selected from CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrTaPt, CoCrPtB, and CoCrPtSiO. In addition, the magnetic layer has a multi-layer structure (for example, CoPtCr/CrMo/CoPtCr, CoCrTaPt/CrMo/CoCrTaPt). Such a structure is obtained by dividing a magnetic film by a nonmagnetic film (for example, Cr, CrMo, CrV) to reduce a noise, as known in the art. The magnetic layer for the magneto-resistive head (MR head) or the giant magneto-resistive head (GMR head) contains impurity elements selected from a group consisting of Y, Si, rare-earth elements, Hf, Ge, Sn and Zn, oxides of these impurity elements in addition to the Co-based alloy.
Further, the magnetic layer may have a granular structure wherein magnetic grains, such as Fe, Co, FeCo and CoNiPt, are dispersed in the nonmagnetic film comprising a ferrite-based material, an iron-rare earth-based material, SiO2, and BN. Further, the magnetic layer may have a recording form of either an in-plane magnetization type or a perpendicular magnetization type.
No restrictions are imposed as to the protection layer also according to this invention. Specifically, the protection layer may be formed by a chromium film, a chromium alloy film, a carbon film, a zirconia film and a silica film and may be successively deposited on the glass substrate together with the underlying layer and the magnetic layer by the use of the known in-line sputtering apparatus. The protection layer may be formed by a single layer or a multi-layer including a plurality of layers of an identical material or different materials.
In addition, the other protection layer, such as a SiO2 film, may be used instead of the above protection layer. Such a SiO2 film may be formed on the chromium film by dispersing colloidal silica fine grains in tetraalkoxysilane diluted with an alcohol-based solvent and thereafter by coating and baking the dispersed grains.
Moreover, the lubricating layer is not restricted to the above. For example, the lubricating layer is formed by diluting perfluoropolyether (PFPE) with a solvent, such as freon-based solvent, and applying it on the medium surface by a dipping method, a spin coating method, or a spraying method, and firing the medium.